The present invention relates to improved diagnostic devices for analyte assay. More particularly it relates to improved devices and methods utilizing filter means for testing biological fluids to detect the presence of analytes such as bacterial, viral, parasitic, or fungal antigens and immunoglobulins, hormones, serum proteins, drugs, and the like.
At the present time there are a number of devices and procedures disclosed for diagnosing the presence of such analytes by means of a reaction occurring on filters but they are either too complex, costly, inaccurate, time-consuming or a combination of such factors.
For example, U.S. Pat. No. 3,888,629 discloses a reaction cell having a matrix pad for carrying out immunoassays. The pad serves as the means for retaining the reagents and as the site in which the reaction occurs as one or more of the fluid reagents are added to the pad and pass therethrough to the absorbent material directly below. In addition to the many time-consuming steps required to process the pad to determine the results of the test, including removing it from the device, such device is essentially limited to isotopic tests. It is not practical for nonisotopic tests such as enzyme-linked immunoassays, since the device requires removal of the absorbent pad for viewing. Moreover, certain biological fluids, such as blood sera, contain particulate and/or colored matter which tend to remain on the surface of the matrix pad and thus make it difficult, if not impossible, to obtain an accurate reading in nonisotopic immunoassay procedures. Further, by passing the reagents directly through the entire surface area of the matrix pad there is often poor separation of the analyte since the absobent pad is very thin (thereby affording only a very short distance for a separation to occur) and there is limited concentration of analyte at any location on or in the pad.
Efforts to improve such device are reflected in U.S. Pat. Nos. 4,246,339 and 4,407,943 which try to limit the area of the fiber through which one or more of the reagents must pass. Here again, however, there is flow directly through the thin filter to the absorbent material below the filter resulting agin in poor separation and difficulty in obtaining accurate readings when specimens are being tested which contain particulate and/or colored matter which is retained on the surface of the filter.
The present invention improves the diagnostic device disclosed U.S. Pat. No. 4,623,461, by forming a substantially cylindrical body portion and a removable cap which has a liquid inlet extending into the cylindrical body portion and includes a conical shaped portion leading to a liquid discharge aperture formed therein. A prefilter may be formed either in the liquid inlet or in a pre-filter container which can be used with the device. The pre-filter container has a substantially cylindrical body which conforms to and can be inserted in the liquid inlet forming part of the removable cap. The container has an open upper end and an associated removable closure, an open bottom end sealed with a frangible material and, if desired, a pre-filter positioned in the container between the upper and lower ends. When liquid is placed in the container, the container may be inserted in the liquid inlet forming part of the cap for the diagnostic device and a puncture device associated with the liquid inlet ruptures the frangible material sealing the lower end and allows the liquid to be funneled to a reaction zone on a filter placed beneath or below the discharge aperture. Various size discharge apertures can be formed in the removable caps thereby allowing a particular cap to be associated with a device for a particular test.